There is a significant amount of description in the art addressing graft polymers, and their methods of preparation, comprising SMA-graft segments. For example, U.S. Pat. No. 3,708,555 addresses the thermal addition reaction of maleic anhydride monomer in liquid styrene with fluid polymers having active hydrogen atoms. Such substrate polymers are said to include such polymers as polypropylene, polyethylene, ethylenepropylene rubber, cispolybutadiene, acrylonitrile-butadiene-styrene, and others having labile or active hydrogens. The purpose of the invention is said to be the provision of carboxyl-containing polymers suitable for melt extrusion as films, sheets, tubes, fibers, etc. having further utility in composites or for dyeability. In one embodiment, the carboxylation reaction is to be conducted in a melt extruder. Similarly, Japanese Open Publication 4800686 addresses the preparation of a propylene-maleic anhydride-styrene graft polymer by introducing polypropylene into maleic anhydride monomer impregnated with 15% benzoyl peroxide in benzene, heated in a 20 vol % styrene solution in toluene.
Additionally certain polymer blends comprising SMA graft compound containing polymers are known. EP-A-336 320 addresses polypropylene blend compositions comprising such components as polypropylene, maleinised polypropylene, polyester resin, epoxy-containing copolymer, ethylenepropylene (-diene copolymer) rubber and modified ethylenic copolymer rubber obtained by graft copolymerizing an unsaturated carboxylic acid (e.g. maleic anhydride) and an unsaturated aromatic monomer (e.g., styrene) onto the rubber. EP-A-335 3394 addresses a thermoplastic resin composition comprising a modified polypropylene obtained by graft copolymerizing an unsaturated carboxylic acid and unsaturated aromatic monomer onto polypropylene, optionally with unmodified polypropylene, a polyester resin, an epoxy group containing copolymer and a modified ethylene- olefin (-nonconjugated diene) copolymer rubber. Styrene is said to be the preferred unsaturated aromatic monomer and maleic anhydride is said to be the preferred carboxylic acid (derivative). Both (maleic anhydride-styrene) -modified polypropylene and -modified ethylene-propylene copolymer rubber are prepared by peroxide-initiated graft copolymerization.
U.S. Pat. No. 4,895,897 describes impact modifiers for polycarbonates comprising the reaction product of an ethylene-propylene elastomer having at least one reactive polar group, typically a hydroxy, epoxy, amine, carboxy or carboxylic-anhyride group, with an oxazoline functionalised polystyrene. The mode of interaction of the polar group and the oxazoline group is not stated but it appears that a cross-linking chain containing at least one nitrogen atom is formed between the ethylene elastomer and the polystyrene.
U.S. Pat. No. 4,742,116 describes a thermoplastic moulding compound based on a rubber-modified copolymer in admixture with ethylene-propylene copolymer (EP) or ethylene-propylenediene terpolymer (EPDM) rubber; the rubber modified copolymer is derived from styrene or alpha-methyl styrene and maleic anhydride, an acrylate or acrylonitrile and is bonded to functionalised EP or EPDM rubber carrying hydroxyl, amide or amine groups.
As indicated above, the graft incorporation of SMA-copolymer segments onto a substrate polymer by graft copolymerization is known as is the potential use for such graft copolymers in various engineering thermoplastic resin blends. However, graft copolymerization, whether conducted by peroxide-initiated or heat-initiated radical formation is subject to several deficiencies. Particularly, it is well known that free-radical formation in the presence of polypropylene can be expected to cause significant molecular weight degradation via chain scission, and in the presence of ethylene-containing-polymers, can be expected to cause similar degradation or cross-linking and gelling in melt processing. Additionally, radical-initiated polymerization of styrene and maleic anhydride, in particular, typically leads to alternating (styrene-co-maleic anhydride) copolymer or copolymer segments. Thus potential improved compatibility to be obtained from pre-selecting SMA molecular weight, molecular weight distribution, comonomer content, comonomer distribution, and ratio of SMA to substrate polymer is largely impossible.